Single Small Extracellular Vesicle (sEV) Quantification by Upconversion Nanoparticles

Cancer-derived small extracellular vesicles (sEVs)are potential circulating biomarkers in liquid biopsies. However,their small sizes, low abundance, and heterogeneity in molecularmakeups pose major technical challenges for detecting andcharacterizing them quantitatively. Here, we demonstrate asingle-sEV enumeration platform using lanthanide-doped upcon-version nanoparticles (UCNPs). Taking advantage of the uniqueoptical properties of UCNPs and the background-eliminatingproperty of total internal reflectionfluorescence (TIRF) imagingtechnique, a single-sEV assay recorded a limit of detection 1.8x106EVs/mL, which was nearly 3 orders of magnitude lower thanthe standard enzyme-linked immunosorbent assay (ELISA). Itsspecificity was validated by the difference between EpCAM-positive and EpCAM-negative sEVs. The accuracy of the UCNP-based single-sEV assay was benchmarked with immunomagnetic-beadsflow cytometry, showing a high correlation (R2> 0.99). The platform is suitable for evaluating the heterogeneous antigenexpression of sEV and can be easily adapted for biomarker discoveries and disease diagnosis

Automated summary

The study demonstrates a single-sEV enumeration platform using UCNPs, which has high sensitivity and specificity, suitable for evaluating the heterogeneous antigen expression of sEV and can be adapted for biomarker discoveries and disease diagnosis.